1. Field of the Invention
The invention relates in general to a pneumatic cylinder powered system for opening and closing a vehicle door and, more particularly, to an adjustable cushioning system for a pneumatic cylinder powered differential engine door opening and closing device for use in passenger transportation vehicles.
2. Description of Related Art
Pneumatic cylinders have been utilized in mechanical systems to convert compressed air into linear reciprocating movement for opening and closing doors of passenger transportation vehicles. An example of this type of door actuating system is shown in U.S. Pat. No. 3,979,790.
Typically, pneumatic cylinders used in this environment consist of a cylindrical chamber, a piston, and two end caps hermetically connected to the cylindrical chamber. The end caps have holes extending therethrough to allow the compressed air to flow into and out of the cylindrical chamber, to cause the piston to move in a linear direction, and to apply either an opening or closing force to the vehicle door.
Pneumatic cylinder/differential engine systems have also been designed for opening and closing doors of passenger transportation vehicles. Examples of these systems are shown in U.S. Pat. Nos. 4,231,192; 4,134,231; and 1,557,684.
It has been determined in some instances that there is a need to slow the movement of the piston at the end of the stroke when opening and/or closing the door. A known technique for slowing this stroke is by restricting the flow of the exhaust air out of the cylindrical chamber. This is commonly known as cushioning the movement of the piston.
A known cushioning system for a pneumatically powered differential engine door opening device is shown schematically in FIG. 1. The differential engine includes a housing comprising a large diameter cylinder 1 and a small diameter cylinder 2, closed at their ends by caps 6 and 7. A large diameter piston 4 is installed in the large cylinder 1 and a small diameter piston 5 is installed in the small cylinder 2. A toothed rack 16 is attached to and extends between the large piston 4 and small piston 5. The toothed rack 16 is engaged with a pinion gear 15. The pinion gear 15 is, in turn, connected to a shaft 14 which drives the mechanism for closing and opening the vehicle door. Linear movement of pistons 4 and 5 causes linear movement of the toothed rack 16. This linear movement is converted into rotational movement of the pinion gear 15 and shaft 14 causing opening and/or closing of the vehicle door as viewed in FIG. 1, movement of the pistons 4 and 5 to the left causes an opening of the doors and movement of pistons 4 and 5 to the right causes a closing of the doors.
As shown in FIG. 1, the right outer side of the small cylinder 2 is connected through a hole 19 in the cap 7 to a reservoir of compressed air that constantly applies a positive pressure to the small piston 5. As shown in schematically in FIG. 2, the cap 6, attached to the outer end of the large cylinder 1, has a chamber 17 including holes 9 and 10 which are connected through a port yy to a three-way valve, which provides connections to a source of compressed air and to an exhaust. During closing of the doors, hole 9 is connected to a source of pressurized air and exhaust hole 10 is closed. Because the surface area of piston 4 is greater than the surface area of piston 5, the pistons 4, 5 move to the right, rotating the pinion gear 15/shaft 14 in a counter-clockwise direction. During an opening stroke, holes 9 and 10 are connected to an exhaust, causing the air to flow out of large cylinder 1. Because the small piston 5 is constantly attached to a source of positive air pressure, the exhausting of the air pressure from within the large cylinder 1 causes the pistons 4, 5 connected by toothed rack 16 to move toward the left within the large and small cylinders 1, 2. This movement to the left rotates the pinion gear 15/shaft 14 in a clockwise direction to initiate opening of the doors.
In this design, cushioning at the end of the opening piston stroke occurs through the use of a small hole 11 having a diameter that is substantially smaller than that of opening xx. This hole 11 is located at a side surface of chamber 17 which provides connection to the inside volume of the chamber of the large cylinder 1. A cylindrical sealing disk 8 is installed between the piston 4 and cap 6 and is supported between two springs 12 and 13. The leftward movement of the pistons 4, 5 causes compression of springs 12 and 13 bringing the disk 8 into contact with a face 17a of chamber 17 forming a seal with the chamber face 17a. Once this seal is achieved, air can no longer exit the chamber of the large cylinder 1 through opening xx into chamber 17 and thus can only exit through hole 11 into chamber 17. Since the diameter of hole 11 is smaller than the diameter of opening xx, the flow of the air out of the large cylinder 1 is restricted, consequently slowing down the speed of the opening piston stroke movement to the left and achieving a cushioning effect during opening of the doors.
U.S. Pat. No. 2,343,316 teaches a pneumatic cylinder/differential engine for power operated doors wherein cushioning occurs near the end of the piston stroke during closing of the doors in order to prevent slamming. In this device, cushioning occurs when a sealing disk contacts with the surface of a cap, causing the exhaust air to flow through a small hole which significantly reduces the rate of flow of the exhaust air from the cylinder housing and decreases the linear speed of the piston.
While the concept of cushioning the end of a piston stroke in a door opening or door closing cycle has been documented, a disadvantage of these systems is that cushioning is always initiated at the same point in the movement of the piston (or at the same position of the piston), and because the linear movement of the piston is transferred to the rotational movement of the output shaft and rotation or linear movement of the powered doors, the doors will always begin to slow at the same point in its path. It is difficult and cost prohibitive to disassemble the pneumatic cylinder, remove the existing components of the cushioning system, replace the spring system supporting the sealing disks, and then reassemble the pneumatic cylinder. Furthermore, if one should select the wrong tensioned spring system, then the process of disassembling/reassembling must be repeated. Another disadvantage of these known systems is that it is impossible to finely adjust the cushion initiation point in the broad range of the linear movement of the piston or rotational movement of the output shaft and, respectively, linear or rotational movement of the power doors.